There are plenty of people using WIN 7 in the world. Main reason-support. Don't forget about all the business computers in the world. Change can be hard for some, particularly those who are shall we say, not tech savvy.
in my personal life I have only 1 machine running windows 7 because I need the use of the laptop RS232 with old 16bit program.
in my work I see plenty of specialized software still unable to run on windows 8 or 10, mostly because the software is expensive (read video surveillance software) and clients refuse to upgrade it....and I have seen this a lot, until the Win 7 computer bombs out and they decide well ok then... lol
I use win 7 on my school laptop. I like it, I think its more utilitarian than 10. I'm also more familiar with it. I use 10 on my gaming PC, but when it comes to getting work done I still prefer to use 7.
I bet there are very few people still using Windows 7 because they prefer t over 10, but if htere are, I'd like to know them.
Simple. Control over my own computer. What patches or updates are installed to my computer or data shared from the same is MY choice to make. Not MS. As a gamer the only reason to care to move to 10 over 7 would be for DX12 and it will be a long time coming before that gets to be a point big enough to concern myself with. Until then MS can suck it and still have to support my "ancient" Windows 7 system.
MS wasted no time in proving what a bad idea forced updates were when they break Win 10 machines until they get around to fixing them. Never mind all of the people that were screwed over with hardware that worked fine on 7 or 8 which no longer worked on 10.
I'll turn the question around. Why would I want to install 10 when 7 works just fine?
You can skip the whole it is more secure bit as I am careful enough about my computing that this isn't a major concern of mine.
Fair bit of our computers are BrandA - VersionB and run SoftwareX1 - VersionY1, SoftwareX2 - VersionY2 and we run it on Windows 7 - upgradeZ
We do that because the client requires it.
That specific software combination has been verified and validated on that specific family of chipsets and while I'm sure running these programs on win10 won't burn down the house down or even change the outcome in a statistically relevant way, it may just mean that none of our models/results can be integrated with the work of any of the other teams. Or worse, it would integrate with a very slight anomaly and influence the surrounding systems.
That would be a bad thing.
Apparently running SoftwareX1 - VersionY1, SoftwareX2 - VersionY2 on the old Windows XP - upgradeZ but on a certain other family of CPUs causes divide by zero errors in specific modules of SoftwareX1 due to the way . . . . certain floating doubles are handled?, although I've never tested this.
Simple: Tried&True. Don't need the latest. Don't need to spend time resolving W10 issues. All W7 issues is been resolved, anytime I got a prob with W7, there are already multiple solutions out there, but most importantly, am running Windows Media Center which W10 dumped.